Quantifying the factors controlling stream-aquifer interactions of ephemeral stream systems and implications for dryland water resource estimation
Abstract
Transmission losses from the beds of ephemeral streams is thought to be the main mechanism of aquifer recharge in arid and semi-arid regions. In these dryland areas, which cover around 40% of the Earth's land surface, groundwater resources are the main source of freshwater. It is commonly assumed that interaction between surface water and groundwater in such environments is unidirectional, and that groundwater does not exert a significant feedback on the rates of transmission losses.
We conducted a series of numerical model experiments of two-dimensional transects to test the sensitivity and degree of interaction between surface and groundwater for typical dryland ephemeral stream geometries, hydraulic properties and flow regimes. Our results indicate that deep water tables, less frequent stream flow events and/or high hydraulic conductivity tend to result in limited interaction between the stream and the groundwater aquifer. Under these conditions, transmission losses eventually reach a constant rate as these parameters increase. With shallower initial depth to the water table, higher stream flow frequency, and/or lower hydraulic conductivity, the 'negative' feedback from the groundwater tends to increase, leading to lower transmission losses. For a typical range of ephemeral stream characteristics, transmission losses are sensitive to feedback from the water table when it exists at depths between 5-10 m. We estimate that 44% of the ephemeral and intermittent river networks located in arid and semi-arid regions globally, overlie shallow aquifers with water table depths less than 5 m, and 55% less than 10 m. Thus, contrary to the widely held belief that ephemeral streams are generally 'disconnected' from groundwater, we suggest that groundwater recharge in such regions could be significantly increased by groundwater abstraction. In this scenario, downstream surface-water resources may also be vulnerable to the associated increase in transmission losses, although the additional water loss may have benefits for reducing flood risk in some locations.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H32E..08C
- Keywords:
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- 0408 Benthic processes;
- BIOGEOSCIENCESDE: 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 1806 Chemistry of fresh water;
- HYDROLOGYDE: 1830 Groundwater/surface water interaction;
- HYDROLOGY